Truck racing tire

ABSTRACT

The invention is directed to a pneumatic radial ply truck tire having a tread with a tread depth D, at least two circumferential grooves dividing the tread into at least a first shoulder circumferential rib, an intermediary circumferential rib, and a second shoulder circumferential rib, the tire being characterized by the tread having a base region disposed at depth D and a cap region over the base region, the base region and the cap region adjoining along a boundary, the cap region comprising a cap rubber composition having properties measured at 23° C. of: elongation of 400 to 500%, true tensile of 77 to 83 MPa, 300% modulus of 9 to 11 MPa, tensile strength of 14 to 15 MPa, shore A hardness of 63 to 68, rebound of 20 to 25%; and the base region comprising a base rubber composition having properties measured at 23° C. of: elongation of 470 to 520%, true tensile of 135 to 150 MPa, 300% modulus of 13 to 15.5 MPa, tensile strength of 22 to 25 MPa, shore A hardness of 63 to 67, rebound 50 to 55%.

This application claims the benefit of co-pending Ser. No. 60/671,568,filed Apr. 15, 2005, and fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

Tires generally have a tread that is well suited for a specific vehicleapplication. Certain tread and reinforcement packages specificallydesigned for a racing truck are well known. The considerations relevantto a tire for such an application are, among others, treadconfiguration, reinforcement package disposition, and materialcomposition. While existing and commercially available tires developedfor truck racing to date have worked well, certain shortcomings in suchtires remain. In particular, existing truck racing tire designs aredeficient in several key areas.

First, the weight and material utilization in currently available truckracing tires is greater than desired resulting in a tire with less thanoptimal temperature and weight characteristics. Another problem is thatexisting tire tread designs for truck racing applications experienceirregular wear in the shoulder region of the tire and offer a less thanoptimal indication of wear. Such irregular shoulder wear results inunpredictable performance and a resultant competitive disadvantage.There is, therefore, a continuing need for a tire providing apredictable and accurate indication of wear in critical regions of thetire.

Still a further problem is that existing tread and tire designs provideless than satisfactory lateral stability and handling and lower thandesired resistance in the event of tread damage. A continuing need,accordingly, exists for a truck racing tire that eliminates or mitigatesthe aforementioned deficiencies.

SUMMARY OF THE INVENTION

The invention is directed to a pneumatic radial ply truck tire having atread with a tread depth D, at least two circumferential groovesdividing the tread into at least a first shoulder circumferential rib,an intermediary circumferential rib, and a second shouldercircumferential rib, the tire being characterized by the tread having abase region disposed at depth D and a cap region over the base region,the base region and the cap region adjoining along a boundary, the capregion comprising a cap rubber composition having properties measured at23° C. of: elongation of 400 to 500%, true tensile of 77 to 83 MPa, 300%modulus of 9 to 11 MPa, tensile strength of 14 to 15 MPa, shore Ahardness of 63 to 68, rebound of 20 to 25%; and the base regioncomprising a base rubber composition having properties measured at 23°C. of: elongation of 470 to 520%, true tensile of 135 to 150 MPa, 300%modulus of 13 to 15.5 MPa, tensile strength of 22 to 25 MPa, shore Ahardness of 63 to 67, rebound 50 to 55%.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a perspective side elevation view of a tire configuredaccording to the present invention.

FIG. 2 is a front elevation view of a portion of the tire of FIG. 1.

FIG. 3 is a transverse sectional view through the tire of FIG. 1.

FIG. 4 is an enlarged section view of the tread portion of the tire ofFIG. 1.

FIG. 5 is a top plan view of a portion of the tire tread.

FIG. 6 is a top plan view of a tire tread portion indicating a wearcondition.

FIG. 7 is a top plan view of a tire tread portion showing notch patternswithin each tread rib.

FIG. 8 is a section view through a notch of FIG. 7 taken along the line8-8.

FIG. 9 is a longitudinal section view through a notch of FIG. 7 takenalong the line 9-9.

FIG. 10 is a transverse section view through a notch of FIG. 7 takenalong the line 10-10.

FIG. 11 is a longitudinal section view through a notch of FIG. 7 takenalong the line 11-11.

FIG. 12 is a transverse section view through a groove of FIG. 7 takenalong the line 12-12.

FIG. 13 is a perspective side elevation view of an alternativeembodiment of a tire configured pursuant to the invention.

FIG. 14 is a front elevation view of a portion of the tire of FIG. 13.

FIG. 15 is a transverse section view through the tire of FIG. 13.

FIG. 16 is an enlarged section view of the tread portion of oneembodiment of a tire of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The truck racing tire of the present invention includes a tread that maybe configured as having a cap/base layer construction in which the capis composed of a relatively softer compound while the base compound iscomposed of a harder compound. With reference to FIG. 16, tire 10includes tread 20 having a tread base 104 disposed at a depth D, andtread cap 102 overlying tread base 104. As shown in the embodiment inFIG. 16, circumferential grooves 106 include tread indicators 108 formedtherein; the depth of the wear indicator is at a depth H which issubstantially at the boundary between the base 104 and the cap 102. Inthis embodiment, the tire 10 is shown as having a tread 20 that issymmetric about the equatorial plane EP; in other embodiments the tiremay be asymmetric as discussed herein.

The tread may be constituted of a layer of a stiff and cool runningtread base rubber compound which facilitates stability and good handlingcharacteristics without heating up the entire tread excessively. Thestiffness is indicated by a high G* and the low heat generation abilityis indicated by low tan delta as well as a high rebound.

On top of the base compound is assembled a layer of relatively higherheat generating and thus soft, high grip cap rubber compound. The stillhigh maximum elongation indicates good integrity of the tread cap aswell as specific durability required for racing.

In one embodiment, the rubber compound formulations for the tread capand tread base regions may be as indicated in the following table, withamounts given in phr: tread cap: tread base: S-SBR (15-25% styrene,35-50% 60-80 polyisoprene 100 vinyl) polyisoprene 20-40 carbon black30-50 carbon black 60-90 silica 10-20 silica 10-20

Along with the materials listed in the above table, the tread base andtread cap compounds further comprise conventional amounts of curativessuch as sulfur, accelerators, zinc oxide, and stearic acid;antidegradants including antioxidants and antiozonants; processing aidsincluding process oils and waxes; and silane coupling agents.

In one embodiment, the tread cap and tread base may have physicalproperties as given in the following table: tread cap: tread base: @ 23°C.: @ 23° C. elongation 400-500% elongation 470-520% true tensile 77-83MPa true tensile 135-150 MPa modulus 300% 9-11 MPa modulus 300% 13-15.5MPa tensile strength 14-15 MPa tensile strength 22-25 MPa shore A 63-68shore A 63-67 hardness rebound 20-25% rebound 50-55% @ 100° C.: @ 100°C.: elongation 300-350% tan delta 10% @ 100° C. 0.115-1.145 true tensile27-32 MPa G* 10% @ 100° C. 1.6-1.7 MPa tensile strength 6.5-8 MPa shoreA 59-59 hardness rebound 50-57% tan delta 10% 0.22-0.27 @ 90° C. G* 10%1.3-1.4 MPa @ 90° C.

More broadly, the rubber compositions for use in the base region and thecap region may contain at least one rubber containing olefinicunsaturation. The phrase “rubber or elastomer containing olefinicunsaturation” is intended to include both natural rubber and its variousraw and reclaim forms as well as various synthetic rubbers. In thedescription of this invention, the terms “rubber” and “elastomer” may beused interchangeably, unless otherwise prescribed. The terms “rubbercomposition”, “compounded rubber” and “rubber compound” are usedinterchangeably to refer to rubber which has been blended or mixed withvarious ingredients and materials and such terms are well known to thosehaving skill in the rubber mixing or rubber compounding art.Representative synthetic polymers are the homopolymerization products ofbutadiene and its homologues and derivatives, for example,methylbutadiene, dimethylbutadiene and pentadiene as well as copolymerssuch as those formed from butadiene or its homologues or derivativeswith other unsaturated monomers. Among the latter are acetylenes, forexample, vinyl acetylene; olefins, for example, isobutylene, whichcopolymerizes with isoprene to form butyl rubber; vinyl compounds, forexample, acrylic acid, acrylonitrile (which polymerize with butadiene toform NBR), methacrylic acid and styrene, the latter compoundpolymerizing with butadiene to form SBR, as well as vinyl esters andvarious unsaturated aldehydes, ketones and ethers, e.g., acrolein,methyl isopropenyl ketone and vinylethyl ether. Specific examples ofsynthetic rubbers include neoprene (polychloroprene), polybutadiene(including cis-1,4-polybutadiene), polyisoprene (includingcis-1,4-polyisoprene), butyl rubber, halobutyl rubber such aschlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadienerubber, copolymers of 1,3-butadiene or isoprene with monomers such asstyrene, acrylonitrile and methyl methacrylate, as well asethylene/propylene terpolymers, also known as ethylene/propylene/dienemonomer (EPDM), and in particular, ethylene/propylene/dicyclopentadieneterpolymers. Additional examples of rubbers which may be used includealkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR,IBR and SIBR), silicon-coupled and tin-coupled star-branched polymers.The preferred rubber or elastomers are polybutadiene and SBR.

In one aspect the rubber is preferably of at least two of diene basedrubbers. For example, a combination of two or more rubbers is preferredsuch as cis 1,4-polyisoprene rubber (natural or synthetic, althoughnatural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

The relatively high styrene content of about 30 to about 45 for theE-SBR can be considered beneficial for a purpose of enhancing traction,or skid resistance, of the tire tread. The presence of the E-SBR itselfis considered beneficial for a purpose of enhancing processability ofthe uncured elastomer composition mixture, especially in comparison to autilization of a solution polymerization prepared SBR (S-SBR).

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

A purpose of using S-SBR is for improved tire rolling resistance as aresult of lower hysteresis when it is used in a tire tread composition.

The rubber composition may optionally include from 0 to about 20 phr of3,4-polyisoprene rubber. The 3,4-polyisoprene rubber (3,4-PI) isconsidered beneficial for a purpose of enhancing the tire's tractionwhen it is used in a tire tread composition. The 3,4-PI and use thereofis more fully described in U.S. Pat. No. 5,087,668 which is incorporatedherein by reference. The Tg refers to the glass transition temperaturewhich can conveniently be determined by a differential scanningcalorimeter at a heating rate of 10° C. per minute.

The cis 1,4-polybutadiene rubber (BR) is considered to be beneficial fora purpose of enhancing the tire tread's wear, or treadwear. Such BR canbe prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The phrase “rubber or elastomer containing olefinic unsaturation” isintended to include both natural rubber and its various raw and reclaimforms as well as various synthetic rubbers. In the description of thisinvention, the terms “rubber” and “elastomer” may be usedinterchangeably, unless otherwise prescribed. The terms “rubbercomposition”, “compounded rubber” and “rubber compound” are usedinterchangeably to refer to rubber which has been blended or mixed withvarious ingredients and materials, and such terms are well known tothose having skill in the rubber mixing or rubber compounding art.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165 MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler.Representative examples of such carbon blacks include N100, N110, N121,N134, N220, N231, N234, N242, N293, N299, N300, N315, N326, N330, N332,N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650,N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991. Thesecarbon blacks have iodine absorptions ranging from 9 to 145 g/kg and DBPnumber ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but notlimited to, particulate fillers including ultra high molecular weightpolyethylene (UHMWPE), particulate polymer gels including but notlimited to those disclosed in U.S. Pat. No. 6,242,534; 6,207,757;6,133,364; 6,372,857; 5,395,891; or 6,127,488, and plasticized starchcomposite filler including but not limited to that disclosed in U.S.Pat. No. 5,672,639.

In one embodiment the rubber composition for use in the tire tread maycontain a conventional sulfur containing organosilicon compound.Examples of suitable sulfur containing organosilicon compounds are ofthe formula:Z-Alk-S_(n)-Alk-Z  IIin which Z is selected from the group consisting of

where R⁶ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;R⁷ is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is aninteger of 2 to 8.

Specific examples of sulfur containing organosilicon compounds which maybe used in accordance with the present invention include:3,3′-bis(trimethoxysilylpropyl) disulfide,3,3′-bis(triethoxysilylpropyl)disulfide, 3,3′-bis(triethoxysilylpropyl)tetrasulfide, 3,3′-bis(triethoxysilylpropyl)octasulfide,3,3′-bis(trimethoxysilylpropyl) tetrasulfide,2,2′-bis(triethoxysilylethyl)tetrasulfide,3,3′-bis(trimethoxysilylpropyl) trisulfide,3,3′-bis(triethoxysilylpropyl)trisulfide,3,3′-bis(tributoxysilylpropyl)disulfide,3,3′-bis(trimethoxysilylpropyl)hexasulfide,3,3′-bis(trimethoxysilylpropyl) octasulfide,3,3′-bis(trioctoxysilylpropyl)tetrasulfide,3,3′-bis(trihexoxysilylpropyl)disulfide,3,3′-bis(tri-2″-ethylhexoxysilylpropyl)trisulfide,3,3′-bis(triisooctoxysilylpropyl) tetrasulfide,3,3′-bis(tri-t-butoxysilylpropyl)disulfide, 2,2′-bis(methoxy diethoxysilyl ethyl)tetrasulfide, 2,2′-bis(tripropoxysilylethyl)pentasulfide,3,3′-bis(tricyclonexoxysilylpropyl)tetrasulfide,3,3′-bis(tricyclopentoxysilylpropyl) trisulfide,2,2′-bis(tri-2″-methylcyclohexoxysilylethyl)tetrasulfide,bis(trimethoxysilylmethyl)tetrasulfide, 3-methoxy ethoxy propoxysilyl3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl)disulfide, 2,2′-bis(dimethylsec.butoxysilylethyl)trisulfide, 3,3′-bis(methyl butylethoxysilylpropyl)tetrasulfide, 3,3′-bis(di t-butylmethoxysilylpropyl)tetrasulfide,2,2′-bis(phenyl methyl methoxysilylethyl)trisulfide, 3,3′-bis(diphenylisopropoxysilylpropyl)tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl)disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl)tetrasulfide, 2,2′-bis(methyldimethoxysilylethyl)trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl)tetrasulfide, 3,3′-bis(diethylmethoxysilylpropyl)tetrasulfide, 3,3′-bis(ethyldi-sec.butoxysilylpropyl)disulfide, 3,3′-bis(propyldiethoxysilylpropyl)disulfide, 3,3′-bis(butyl dimethoxysilylpropyl)trisulfide, 3,3′-bis(phenyl dimethoxysilylpropyl)tetrasulfide, 3-phenylethoxybutoxysilyl 3′-trimethoxysilylpropyl tetrasulfide,4,4′-bis(trimethoxysilylbutyl)tetrasulfide,6,6′-bis(triethoxysilylhexyl)tetrasulfide, 12,12′-bis(triisopropoxysilyldodecyl)disulfide, 18,18′-bis(trimethoxysilyloctadecyl)tetrasulfide,18,18′-bis(tripropoxysilyloctadecenyl) tetrasulfide,4,4′-bis(trimethoxysilyl-buten-2-yl)tetrasulfide,4,4′-bis(trimethoxysilylcyclohexylene)tetrasulfide,5,5′-bis(dimethoxymethylsilylpentyl) trisulfide,3,3′-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide,3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.

In one embodiment, the sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl)sulfides. In oneembodiment, the sulfur containing organosilicon compounds are3,3′-bis(triethoxysilylpropyl)disulfide and3,3′-bis(triethoxysilylpropyl)tetrasulfide. Therefore, as to formula II,Z may be

where R⁷ is an alkoxy of 2 to 4 carbon atoms, alternatively 2 carbonatoms; alk is a divalent hydrocarbon of 2 to 4 carbon atoms,alternatively with 3 carbon atoms; and n is an integer of from 2 to 5,alternatively 2 or 4.

In another embodiment, suitable sulfur containing organosiliconcompounds include compounds disclosed in U.S. Pat. No. 6,608,125. Asdisclosed in U.S. Pat. No. 6,608,125, these sulfur containingorganosilicon compounds are of the formula G-C(══O)—S—CH₂CH₂CH₂SiX₃wherein each X is an independently selected RO— group wherein each R isindependently selected from the group consisting of hydrogen, alkyl thatmay or may not contain unsaturation, alkenyl groups, aryl groups, andaralkyl groups, such moieties other than hydrogen having from 1 to 18carbon atoms, and G is a monovalent alkyl of from 6 to 8 carbon atoms.In one embodiment, the sulfur containing organosilicon compoundsincludes 3-(octanoylthio)-1-propyltriethoxysilane,CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commerciallyas NXT™ from GE Silicones.

In another embodiment, suitable sulfur containing organosiliconcompounds include those disclosed in U.S. Patent Publication2003/0130535. As disclosed in U.S. Patent Publication 2003/0130535,these sulfur containing organosilicon compounds are of the formulas IIIor IV

wherein: R is a methyl or ethyl group;

R′ is identical or different and is a C₉C₃₀ branched or unbranchedmonovalent alkyl or alkenyl group, aryl group, aralkyl group, branchedor unbranched C₂-C₃₀ alkyl ether group, branched or unbranched C₂-C₃₀alkyl polyether group or R′″₃Si, where R′″ is C₁-C₃₀ branched orunbranched alkyl or alkenyl group, aralkyl group or aryl group, R″ is abranched or unbranched, saturated or unsaturated, aliphatic, aromatic ormixed aliphatic/aromatic divalent C₁-C₃₀ hydrocarbon group;

X is SH where n=1 and m=1, S where n=2 and m=1-10 and mixtures thereof,S(C══O)—R′″ where n=1 and m=1 or H where n=1 and m=1;

R″ may mean CH₂, CH₂CH₂, CH₂CH₂CH₂, CH₂CH₂CH₂CH₂, CH(CH₃), CH₂CH(CH₃),C(CH₃)₂, CH(C₂H₅), CH₂CH₂CH(CH₃), CH₂CH(CH₃)CH₂ or

In one embodiment, the sulfur containing organosilicon compound is offormula III, R is ethyl, R′ is C₁₂-C₁₄ alkyl, R″ is CH₂CH₂CH₂, X is SH,n is 1 and m is 1. In one embodiment, the sulfur containingorganosilicon compound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agentis elemental sulfur. The sulfur-vulcanizing agent may be used in anamount ranging from 0.1 to 8 phr, alternatively with a range of from 0.5to 6 phr. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Representativeprocessing aids may be for example, process oils including aromatic,paraffinic, napthenic oils, vegetable oils, and low PCA oils, such asMES, TDAE, SRAE and heavy naphthenic oils. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

With reference now to FIGS. 1, 2, and 3, one alternative embodiment of atruck racing tire 10 is depicted in accordance with the subjectinvention, preferably for use on either the front or rear axles of aracing truck. While intended specifically for truck racing tires, theprinciples of the invention will find alternative uses in otherapplications apparent to those skilled in the art. The followingdefinitions will aid in understanding of the drawings:

“Axial” and “axially” are used herein to refer to lines or directionsthat are parallel to the axis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim.

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber over the plies, but including the beads.

“Carcass plies” comprise parallel longitudinal reinforcing members whichare wrapped around the beads.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection.

“Crown” refers to that portion of the tire within the width area of thetread in the vicinity of the tread.

“Design feature” includes enough of the tread pattern to constitute atleast one notch on each tread region.

“Equatorial plane” refers to the plane perpendicular to the tire's axisof rotation and passing through the center of its tread. “Tread ShoulderRib” refers to portion of tread adjacent the tire sidewall.

“Footprint” refers to the contact patch or area of contact of the tiretread with a flat surface at zero speed and under normal load andpressure or under specified load, pressure and speed conditions.

“Global treadwear” refers to normal treadwear, generally evenlydistributed around a tire.

“Irregular treadwear” refers to uneven patterns of wear, sometimeslocalized where one side or edge of the tread wears faster than another.

“Lateral Edge” means the axially outermost extremes of the tread.

“Radial” and “radially” are used to mean directions radially toward oraway from the axis of rotation of the tire.

The tire 10 has a tread 20 and a casing 12. The casing 12 has twosidewalls 14,16 one or more radial plies 18 extending from and wrappedabout two annular beads 13 and a belt reinforcement structure 15 locatedradially between the tread 20 and the plies 18.

The plies 18 and the belt reinforcement structure 15 are cord reinforcedelastomeric material, the cords being preferably steel wire filamentsand the elastomer preferably being a vulcanized rubber material.Similarly, the annular beads 13 have steel wires wrapped into a bundleknown as the bead core.

The liner 19 is a component of preferably halobutyl rubber that forms asomewhat air impervious chamber to contain the air pressure when thetire 10 is inflated.

As shown, the belt structure of the preferred embodiment tire has threecord reinforced belts 22, 24, and 26. Additionally, the beltreinforcement structure 15 includes a gum strip of rubber material 28.The ply turnup 30 in the bead area is reinforced with a flipper 32,chipper 34, gum and fabric chafers 36,38, gum strips 40 and elastomericwedges 42 and a plurality of elastomeric strips or wedges 44 in thelateral extremes of the belts 15 in proximity of the tread lateral edge.Although not required to the practice of the inventive concept, thesefeatures are disclosed as features employed in the preferred embodiment.

The tread 20 preferably has a pair of circumferentially continuousgrooves 46, 48 which divide the tread 20 into three tread ribs,including a pair of shoulder ribs 50, 54 separated by an intermediaterib 52. The tread 20 is asymmetrically configured in that the shoulderrib 54 is wider than the shoulder rib 50. The equatorial plane of thetire, as best seen in FIG. 3, extends off center through the center rib52. The wide shoulder rib 54 is situated on the outside on a front axleof a truck or on the inside when mounted on a rear axle to optimizevehicle stability and handling. The rib 54 is configured having arounded lateral edge surface 56 and the rib 50 is provided with anangled lateral edge surface 58 which optimize vehicle stability andhandling. More grooves may be used dependent on the width of the treadand other design considerations such as, but not limited to, thealternatively configured tread depicted in FIGS. 13-15.

As shown in FIGS. 1 through 3, the tire 10 uppermost belt 26 is ofrelatively reduced distance from the tread 20, on the order of 2 to 5mm. Additionally, the tread 20 is configured to be relatively reducedthickness, preferably dimensioned as 5 mm. The reduced thickness oftread and undertread between the tread 10 and belt 26 reduces materialcontent, for optimized handling, stability, and temperature control.

In use, the tire ribs 50, 52, and 54 wear and the rib depth is reduced.In order to indicate tread wear, a respective pattern ofcircumferentially spaced notches 60, 62, 64 are formed therein,respectively. As the tread wears, the notches are reduced in depth andeventually eliminated as depicted in FIG. 6. In practice, the tread willgenerally wear at different rates causing the notches to reduce in depthaccordingly. By monitoring the depths of the notches, the wear patternand level of wear may be ascertained. Each notch 60, 62, 64, as shown inFIGS. 7 through 12, are generally U-shaped in cross-section and has aninitial depth of 3.5 mm. The depth of the grooves 46, 48 (see FIG. 12)is preferably on the order of 5.1 mm. Wear indicators in the form ofmarkings are placed in sidewalls of the grooves (not shown) at a depthequivalent to the depth of notches 60, 62, 64 (preferably 3.5 mm) thusproviding an additional indication of wear as the tread 20 is reduced.It will further be noted that the notch pattern in each rib 50, 52, 54is preferably distinctive to each rib and the notches may be oriented ina staggered configuration from rib to rib or, as shown with regard torib 54, and/or oriented at an angle relative to the equatorial plane ofthe tire. By varying the distribution and orientation of the notchesfrom tire rib to tire rib and around the circumference of the tire, aclearer indication of wear pattern and extent may be determined.

Additionally, it is preferred that the tread 20 be configured as havinga cap/base layer construction in which the cap is composed of arelatively softer compound while the base compound is composed of aharder compound. Such compounds are commercially available. The softercap compound provides high griping and handling performancecharacteristics while hard and cool running compound in the tread baseimproves tire lateral stability and handling, reduces heat generation,and improves the tire's resistance characteristics in the event thetread is damaged. Location of the cap and base boundary is furtherpreferably at 3.5 mm from the tread surface so as to allow the user todetect the harder base layer when the tread cap is worn away. FIG. 4illustrates in broken line the boundary between the softer cap andharder base at a depth “D”. Thus, the dual composition of the treadalong a boundary line placed at the same depth as the notch and groovedepths provides yet a further indication of tire wear. Such a redundancyincreases the likelihood that the driver will immediately detect anunsafe wear condition within the tire.

FIGS. 13-15 illustrate one alternative embodiment of invention in whichfour ribs 66, 68, 70, and 72 are provided, outermost shoulder ribs 66,72 having a rounded shoulder 74 and a squared shoulder region,respectively. Notches 78, 80, 82, 84, as in the previous embodiment, areincorporated into the ribs for heat and water evacuation as well as fortread wear indication. Grooves 86, 88, and 90 extend circumferentiallyand define the ribs.

From the foregoing, it will be apparent that the subject tire for truckracing in a unique belt package, tread pattern and composition providesenhanced handling, tire grip, and tread endurance while optimizingweight. The wider shoulder rib provides for good handling and highlateral stability and the circumferential grooves for water and heatevacuation. The tread wear indicators in the grooves provide for wearfollow-up and are at a depth common to the depth of the rib notches. Thenotches in the ribs provide gripping on dust or water and also, beingdistributed in select patterns circumferentially, provide for localizedwear detection. The rounded shoulder is placed preferably outside on afront axle and inside on a rear axle to optimize vehicle stability andhandling.

In using three belts, rather than a greater number, weight is reducedand better temperature dispersion is achieved. Moreover, the undertreadthickness is reduced for optimized weight and temperaturecharacteristics. Use of a softer cap composition and harder basecomposition in the tread acts to prevent rapid damage to the tire andwear from reaching the carcass. The point in time when the tire is wornwill be perceived by the user due to the position of the boundarybetween the softer cap and the harder tread base at a depth common tothe notch tread wear indicators.

Variations in the present invention are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed which will be within the full intended scope of the inventionas defined by the following appended claims.

The invention is further illustrated by the following nonlimitingexample.

EXAMPLE

Tread cap and base compounds are contemplated to be fabricated using thecompound recipes as shown in Table 1. Cured compounds are contemplatedto be tested and expected to have properties within the ranges shown inTable 2. TABLE 1 tread cap: tread base: S-SBR (15-25% 70 phrpolyisoprene 100 phr styrene, 35-50% vinyl) polyisoprene 30 phr carbonblack (ASTM N100) 42 phr carbon black 77 phr cure promoters 10.7 phr(ASTM N300) cure promoters 10.7 phr antidegradants 6.5 phrantidegradants 4.5 phr processing aids 2 phr processing aids 37 phrsilica 15 phr sulfur 0.4 phr silane coupling agent 2 phr silane coupling3 phr sulfur 0.9 phr agent silica 15 phr

TABLE 2 tread cap: tread base: @ 23° C.: @ 23° C. elongation 400-500%elongation 470-520% true tensile 77-83 MPa true tensile 135-150 MPamodulus 300% 9-11 MPa modulus 300% 13-15.5 MPa tensile strength 14-15MPa tensile strength 22-25 MPa shore A 63-68 shore A 63-67 hardnessrebound 20-25% rebound 50-55% @ 100° C.: @ 100° C.: elongation 300-350%tan delta 10% @ 100° C. 0.115-1.145 true tensile 27-32 MPa G* 10% @ 100°C. 1.6-1.7 MPa tensile strength 6.5-8 MPa shore A 59-59 hardness rebound50-57% tan delta 10% 0.22-0.27 @ 90° C. G* 10% 1.3-1.4 MPa @ 90° C.

1. A pneumatic radial ply truck tire having a tread with a tread depthD, at least two circumferential grooves dividing the tread into at leasta first shoulder circumferential rib, an intermediary circumferentialrib, and a second shoulder circumferential rib, the tire beingcharacterized by: the tread having a base region disposed at depth D anda cap region over the base region, the base region and the cap regionadjoining along a boundary, the cap region comprising a cap rubbercomposition having properties measured at 23° C. of: elongation of 400to 500%, true tensile of 77 to 83 MPa, 300% modulus of 9 to 11 MPa,tensile strength of 14 to 15 MPa, shore A hardness of 63 to 68, reboundof 20 to 25%; and the base region comprising a base rubber compositionhaving properties measured at 23° C. of: elongation of 470 to 520%, truetensile of 135 to 150 MPa, 300% modulus of 13 to 15.5 MPa, tensilestrength of 22 to 25 MPa, shore A hardness of 63 to 67, rebound 50 to55%.
 2. A tire according to claim 1 further characterized in that atleast one groove has a wear indicator formed therein at a preselecteddepth.
 3. A tire according to claim 2 further characterized in that theboundary between the base region and the cap region is substantially atthe preselected wear indicator depth within the one groove.
 4. A tireaccording to claim 3 further characterized in that at least one treadregion has at least one notch formed therein extending to thepreselected wear indicator depth.
 5. A tire according to claim 1 furthercharacterized by at least one belt reinforcement structure locatedradially from the tread, the belt reinforcement structure comprisingthree belts.
 6. A tire according to claim 5 wherein the nominal distancebetween the tread and an uppermost belt ranges between 2 and 5 mm.
 7. Atire according to claim 1 wherein further characterized by a pluralityof elongate notches formed to extend into the tread first shoulder rib,second shoulder rib, and intermediary rib in respective circumferentialpatterns.
 8. A tire according to claim 7, wherein further characterizedby the circumferential patterns of first shoulder rib, the secondshoulder rib, and the intermediary rib are mutually distinctive.
 9. Atire according to claim 7 wherein the notches in the second shoulder ribextend at an oblique angle relatively to the equatorial plane of thetire.
 10. A tire according to claim 7 wherein the notches in the firstshoulder rib extend substantially normal to the equatorial plane of thetire.
 11. A tire according to claim 7 wherein a plurality of notchesextend to the boundary depth D of the tread.
 12. An asymmetric pneumaticradial ply truck tire having a tread with a tread depth D, at least twocircumferential grooves dividing the tread into at least a firstshoulder circumferential rib, an intermediary circumferential rib, and asecond shoulder circumferential rib, the tire being characterized by thefirst shoulder rib having width wider than the second shoulder rib and asubstantially rounded upper surface across an outer edge region; thesecond shoulder rib having a substantially flat upper surface across anouter edge region; and the tread having a first wear indicator disposedwithin at least one circumferential groove and a second wear indicatordisposed within a rib for confirmation of tread wear.
 13. A tireaccording to claim 12, wherein further characterized by the second wearindicator comprising a tread base region disposed at depth D constructedfrom relatively harder material and a cap region over the base regionconstructed from relatively softer material, the base region and the capregion adjoining along a boundary.
 14. A tire according to claim 13,wherein the first wear indicator within the at least one groove is atthe depth of the boundary between the base region and the cap region.15. A tire according to claim 12, wherein further characterized by thesecond wear indicator comprising at least one notch formed to extendinto at least one rib to a depth substantially corresponding to thedepth of the first wear indicator.
 16. A tire according to claim 12,wherein further characterized by at least one belt reinforcementstructure located radially from the tread, the belt reinforcementstructure comprising three belts.
 17. A tire according to claim 12,wherein further characterized by the first shoulder rib having asubstantially rounded upper surface across an outer edge region and thesecond shoulder rib having a substantially flat upper surface across anouter edge region.
 18. A tire according to claim 12, wherein furthercharacterized by a plurality of elongate discrete notches formed toextend into the tread first shoulder rib, second shoulder rib, andintermediary rib in respective circumferential patterns.
 19. A tireaccording to claim 18, wherein further characterized by at least onenotch in each circumferential pattern extends to a depth correspondingwith the depth of the first wear indicator within the at least onecircumferential groove.
 20. A tire according to claim 1 furthercharacterized in that the first shoulder rib has a width wider than thesecond shoulder rib and a substantially rounded upper surface across anouter edge region; and the second shoulder rib has a substantially flatupper surface across an outer edge region.